The role of hypothalamic norepinephrine - (NE) and dopamine - (DA) containing neurons in the regulation of LH and prolactin will be studied. The NE and DA concentrations of microdissected median eminences, suprachiasmatic (SCN) arcuate, and medial preoptic nuclei were measured using the catecholamine-O-methyltransferase assay. Between the morning and afternoon of proestrus a 3-fold increase in NE was observed only in the SCN. The uptake and synthesis rate of NE and DA will be determined in these hypothalamic nuclei throughout the estrous cycle. The uptake rate will be measured in vitro by following the rate of accumulation of 3H-catecholamine in hypothalamic nuclei microdissected from unfrozen brain slices. The synthesis rates will be estimated in vivo by measuring the rate of incorporation of intraventricularly administered 3H-tyrosine into NE and DA. Tuberoinfundibular DA neurons play a central role in the regulation of prolactin secretion. Simultaneous measurements of prolactin and DA levels in cavernous sinus blood will be performed in awake, unstressed dogs. Establishment of an inverse relationship between the levels of DA and prolactin in the veinous drainage of the anterior pituitary would clearly establish that DA is a physiological prolactin inhibitory factor. Apparent DA receptors in the anterior pituitary become hypersensitive to apomorphine following long term lesions of the medial basal hypothalamus. Approximately 100-fold less apomorphine inhibits prolactin secretion in vivo or in vitro from long-term lesioned rats. The pharmacological characteristics and time course of the onset of hypersensitivity will be determined. Whether changes in receptor sensitivity play a role in the regulation of nocturnal increases in prolactin secretion during pseudopregnancy or lactation-related changes will be studied. Further studies will evaluate the possibility that supersensitivity of anterior pituitary DA receptors is involved in the sequelae of events in women with hyperprolactinemia.